A long-term goal of my laboratory is to understand the biochemical mechanisms underlying sperm motility and fertilization. In spermatozoa, where little protein synthesis occurs, protein phosphorylation is a major mechanism for regulating cellular functions. While it is known that changes in protein phosphorylation control motility initiation and fertilization, our knowledge of signaling pathways regulating these changes is limited. This proposal centers on a signaling enzyme in spermatozoa, the serine/threonine phosphatase PP1gamma2. It is a key enzyme in spermatogenesis and regulation of mature sperm function. Knowing how this enzyme works at the biochemical and molecular levels will contribute to our understanding of male gamete function. Protein purification and sequencing have enabled us to identify a number of potential PP1gamma2 binding and regulatory proteins. Immunoprecipitation and binding studies with recombinant proteins showed that two of these regulatory proteins are sds22 and protein 14-3-3 - discovered for the first time in spermatozoa. These polypeptides, which have critical functions in somatic cells, have novel roles in regulating male gamete function. In addition to changes in its binding to regulatory proteins, PP1gamma2 phosphorylation is increased during sperm maturation in the epididymis. The central hypothesis in this proposal is that the regulated action of PP1gamma2 is critical for sperm maturation, motility initiation, and other essential sperm functions. We will use biochemical and molecular approaches to characterize, at the mechanistic level, how phosphorylation and binding interactions between PP1gamma2 and its regulatory proteins relate to sperm motility and fertilizing ability. Aside from its basic importance to male gamete biology, this study has potential applications in the diagnosis and treatment of male infertility and in the development of novel approaches to male contraception.